This invention relates to surgical bone cement compositions and more particularly to bone cement compositions having anaesthetic properties, and to methods for producing analgesia.
Polymer based surgical bone cements have been used for many years to fill voids in bones and to improve fixation of implanted orthopaedic prosthetic devices. Typically such cements contain polymers or copolymers of alkyl methacrylate and/or copolymers of methyl methacrylate with methyl acrylate or styrene. The liquid compound consisting of esters of acrylic or methacrylic acid (typically methyl methacrylate) is packaged in an ampoule, possibly with additives such as premature polymerization preventers such as hydroquinone, and curing promoters such as N,N-dimethyl-p-toluidine. A polymerization initiator, typically an organic peroxy compound such as powdered benzoyl peroxide, is combined with the polymeric component and a radiopacifier (such as barium sulphate or zirconium dioxide) for rendering the bone cement opaque to X-rays. The polymeric materials are generally sterilized by either irradiation or gas sterilization. In use, typically a bone is cut and prepared to receive a surgical implant and then the liquid and dry components of the cement, contained in the ampoule and powder bag are mixed together to form a paste which can then be applied by the surgeon to the cut bone. The implant can then be set in the paste which, when fully polymerized, forms a continuous solid interface between the implant and the bone.
It is also known to incorporate therapeutic or diagnostic substances into the bone cement for various purposes. For example, U.S. Pat. No. 4,900,546, issued Feb. 13, 1990, to Posayn Dowty et al., teaches the incorporation of antibiotics such as gentamycin, penicillin and tetracycline; anti-cancer drugs; anti-inflammatory drugs; immuno-stimulants; immuno-suppressants; osteogenic promoters and diagnostic substances such as radioactive tracers. While some anti-inflammatory drugs may have analgesic properties, such compounds are not anaesthetics.
Although local anaesthetics, such as lidocaine and prilocaine are known to have potent anti-microbial activity (anti-bacterial and anti-fungal), when used in relatively high dosages (0.5-2% solution) (J. Infect. Diseases, 121:597-607, 1970), heretofore such anaesthetic compounds have not been incorporated into bone cements for the promotion of anaesthesia. It has now been found that substantial pain relief can be achieved by incorporating into a known bone cement composition a local anaesthetic at a dosage level several orders of magnitude lower than would be required to achieve an anti-microbial effect with such anaesthetic.
An object of the present invention is to provide novel bone cement compositions which incorporate an anaesthetic, and have analgesic properties. Another object of this invention is to provide a method for producing analgesia in the vicinity of a bone surgery site.
By a broad aspect of this invention, there is provided an anaesthetic bone cement comprising a bone cement composition including an effective amount up to about 5% by weight of an anaesthetic, preferably a local anaesthetic.
By a preferred aspect of this invention, there is provided an anaesthetic bone cement composition comprising: (a) a liquid monomeric (meth)acrylate composition; (b) a powder comprising at least one of a homopolymer and a copolymer of methyl methacrylate containing an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of said bone cement composition of a local anaesthetic.
An anaesthetic bone cement composition in accordance with the invention includes a local anaesthetic in a physical form such as, for example, liquids and solids, and a chemical form such as, for example, acids and bases. A local anaesthetic is released from the bone cement in a preselected characteristic release profile that is determined by at least one of chemical form and physical form of the anaesthetic. An anaesthetic bone cement composition according to the invention comprises an anaesthetic in an amount between about 0.007% and about 5% by weight of said cement composition. An anaesthetic bone cement composition according to the invention can comprise a local anaesthetic provided in at least two different forms, the forms being, for example, acids, bases, solids, and liquids. Also in accordance with the invention, an anaesthetic bone cement composition can comprises a combination of at least two anaesthetics selected from the group consisting of lidocaine, bupivacaine, prilocaine and tetracaine. When a combination of two or more different anaesthetics are included in the bone cement composition of the invention, they can be in two different forms, the forms being selected from the group consisting of acids, bases, solids, and liquids, or they can be of the same form.
By another aspect of this invention, there is provided a process for producing an anaesthetic bone cement comprising combining: (a) a liquid monomeric (meth)acrylate; (b) a powdered component comprising at least one of a homopolymer and a copolymer of methyl methacrylate, an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of a local anaesthetic.
By yet another aspect of this invention there is provided a method for producing analgesia at an orthopaedic implant site in a patient, comprising cutting and preparing a bone at said site to receive said implant and applying to said prepared bone a bone cement composition comprising: (a) a liquid monomeric (meth)acrylate composition; (b) a powder comprising at least one of a homopolymer and a copolymer of methyl methacrylate containing an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of said bone cement composition of a local anaesthetic.
According to the method of the invention, a local anaesthetic included in a bone cement composition can be in a physical form such as, for example, liquids and solids, and a chemical form such as, for example, acids and bases. A local anaesthetic is released from the bone cement in a preselected characteristic release profile that is determined by at least one of chemical form and physical form of the anaesthetic. An anaesthetic bone cement composition according to the method of the invention comprises an anaesthetic in an amount between about 0.007% and about 5% by weight of said cement composition. An anaesthetic bone cement composition according to the method of the invention can comprise a local anaesthetic provided in at least two different forms, the forms being, for example, acids, bases, solids, and liquids. Also in accordance with the method of the invention, an anaesthetic bone cement composition can comprises a combination of at least two anaesthetics selected from the group consisting of lidocaine, bupivacaine, prilocaine and tetracaine. When the method of the invention involves use of a combination of two or more different anaesthetics, they can be in two different forms, the forms being selected from the group consisting of acids, bases, solids, and liquids, or they can be of the same form.